Rollers for conveyor belts are arranged so that the conveyor belt travels thereover in a downstream belt travel direction and path. However, conveyor belts can tend to meander or mistrack toward one side or the other of the rollers such as due to uneven loads carried by the belt. Conveyor belt tracking devices have been developed that respond to belt mistracking to attempt to redirect the belt back to its correct travel path substantially central on the conveyor rollers.
Conveyor belt trackers have commonly included a pivoting system that provides pivoting of one or more idler or tracking rollers in response to mistracking of the conveyor belt. In response to the belt mistracking, the idler roller is shifted so that the one end portion of the idler roller shifts downstream. So configured, the idler roller steers the conveyor belt back toward the desired belt travel path. One such belt tracker is disclosed in U.S. Pat. No. 2,225,276 to Parker and includes an idler roller that is pivotal about a pivot axis that is inclined in the downstream direction. In this regard, when a conveyor belt mistracks toward one end portion of the idler roller, the drag forces acting downstream on the idler roller end portion increase urging the end portion to shift downstream, while the downstream tilt of the pivot axis causes the idler roller end portion to also shift downwardly under the increased weight of the mistracked belt passing over the end portion. Thus Parker's belt tracker utilizes the weight of the conveyor belt and drag forces acting on the end portion toward which the belt is mistracking to energize the idler roller to pivot about the pivot axis. The system described by Parker, however, is largely ineffective at influencing and changing the path of the belt in applications and conditions where condensation, ice, or debris would accumulate at the interface between the idler roller and the conveyor belt.
Applicant's assignee herein provided a previous version of a PT Smart™ belt tracker that had both sensor rollers and an idler roller. The sensor rollers were oriented upstream from the idler roller and arranged on either side of the belt. The sensor rollers were operatively connected to the idler roller so that when belt mistracking caused the belt to engage one of the sensor rollers, this engagement force was transferred to the idler roller to provide it energy for pivoting to correct the path of the mistracking belt. In this regard, the idler roller was positioned downstream of its pivot axis and the pivot axis was inclined in the upstream direction, so that upon the mistracking conveyor belt edge providing sufficient energy to the sensor roller through engagement with the sensor roller toward which it was mistracking, the corresponding end portion of the idler roller would shift upwardly and downstream. In this manner, the upwardly shifted end portion of the roller would engage the conveyor belt edge passing thereover to increase the tension in the belt edge and urge the conveyor belt to shift toward the belt travel direction. In other words, the conveyor belt would tend to move away from the edge having high tension and toward the opposite conveyor belt edge with lower tension.
While effective, a substantial amount of force was required from the belt edge engaging the sensor roller to shift the one end portion upwardly in the previous PT Smart™. This force could more quickly wear the belt edges as they engaged the sensor rollers. In addition, the sensor arms extended far upstream of the idler roller to maximize the torque about the pivot axis from the energizing forces between the belt edge and the sensor rollers. These long torque arms required a significant amount of outward lateral displacement of the sensor rollers to generate a sufficient shifting of the tracking roller necessary to correct the path of the mistracking belt. Because conveyor belt systems can be utilized with tight lateral constraints on either side, the previous PT Smart™ was not optimal for such applications.
In addition, laterally inward shifting of the end portion of the tracking roller underneath the mistracking edge of the belt allowed the mistracking edge of the conveyor belt shifting laterally in the opposite direction to shift off of and out of engagement with the idler roller. However, steering the conveyor belt by shifting the end portion located at the side of the belt tracker toward which the belt is mistracking downstream relies on contact and corresponding friction between the conveyor belt and the idler roller. Thus, in these systems, because the conveyor belt would shift off the end of the idler roller, the amount of contact between the belt and roller was reduced, thereby reducing the effectiveness of the steering mechanism for correcting the direction of the mistracking belt. This is particularly problematic when the interface between the belt and idler roller gets wet since the already reduced surface contact and corresponding frictional forces between the belt and roller are further reduced making it more difficult for the idler roller to effectively influence and change the path of the belt.